Nickel-chromium alloys adapted for use in contact with molten glass

ABSTRACT

NICKEL-BASE ALLOYS CONTAINING CORRELATED PERCENTAGES OF CARBON, CHROMIUM, TUNGSTEN, TANTALUM AND PREFERABLY ZIRCONIUM AFFORD GOOD CORROSION RESISTANCE AND EXHIBIT HIGHLY SATISFACTORY ELEVATED TEMPERATURE PROPERTIES (CIRCA 1080*C.), CHARACTERISTICS WHICH RENDER THE ALLOYS PARTICULARLY SUITABLE FOR USE IN CONTACT WITH SUCH MEDIA AS MOLTEN GLASS.

United States Patent 3,552,952 NICKEL-CHROMIUM ALLOYS ADAPTED FOR USE INCONTACT WITH MOLTEN GLASS Stuart Walter Ker Shaw, Coldfield, England,assignor to The International Nickel Company, Inc., New York, N.Y., acorporation of Delaware No Drawing. Filed Nov. 26, 1968, Ser. No.779,207 Claims priority, application Great Britain, Dec. 4, 1967,54,997/67; Aug. 14, 1968, 38,869/68 Int. Cl. C22c 19/00 U.S. Cl. 75-17117 Claims ABSTRACT OF THE DISCLOSURE Nickel-base alloys containingcorrelated percentages of carbon, chromium, tungsten, tantalum andpreferably zirconium afford good corrosion resistance and exhibit highlysatisfactory elevated temperature properties (circa 1080 C.),characteristics which render the alloys particularly suitable for use incontact with such media as molten glass.

As is generally known by those skilled in the art, a considerable numberof diverse metals and alloys have been proposed and used for hightemperature applications, applications which also often demandexceptional resistance to various corrosive media. Illustrative of thisare the many situations in which the handling of molten glass isencountered. In historical perspective it has been the precious metalsand alloys thereof which have found extensive use, generally speaking,in molten glass environments but, as would be expected, the relativelyhigh cost of such materials has always been an inherent drawback.

In the continuous search for less expensive materials, a variety ofalloys has been investigated, and the nickelbase materials have receivedparticular attention in view of their generally good corrosion behaviorand ability to resist the effects of high temperature. One such alloy,used as spinners in the production of glass fibers, contains about 52%nickel, 25% chromium, 5% tungsten, 0.5% carbon, the balance being iron.However, while this alloy has given good service, spinners fabricatedtherefrom cannot be gainfully used at temperatures exceeding about 1030C. (even at 1030 C. their life under actual operating conditions isrelatively short). This aspect serves to emphasize that more than goodcorrosion resistance and lower cost is necessary. For if the morestringent conditions brought about by higher operating temperatures areto be successfully met, a new combination of elevated temperaturecharacteristics is required. Accordingly, there is need for an alloyhaving improved properties such that it can be used at temperatures wellabove 1030 C. e.g. 1080 C. or above (or which has a longer useful lifeat lower operating temperatures).

It has now been discovered that certain nickel-base alloys containingspecial amounts of carbon, chromium, tungsten, tantalum and zirconium,provide an improved combination of stress rupture characteristics andresistance to creep at temperatures above 1030 C., e.g., 1080 C. orhigher, while concomitantly manifesting a high degree of resistance tothe corrosive and erosive action of molten glass.

It is an object of the present invention to provide novel and usefulnickel-base alloys possessing satisfactory elevated temperatureproperties.

Another object of the present invention is to provide nickel-base alloyswhich greatly resist the corrosive and erosive efiects of molten glass.

A further object of the present invention is to provide articles ofmanufacture fabricated from alloys of the invention for use in contactwith molten glass.

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Other objects and advantages will become apparent from the followingdescription.

In accordance with the invention, an optimum combination of propertiescan be achieved with the preferred alloy contemplated herein containing(by weight) from about 0.3% to 1% carbon, from about 25% to 35%chromium, from about 3% to about 8% tungsten, from about 2% to 8%tantalum, a small but effective amount, e.g. about 0.1% and up to about0.5% zirconium, up to 0.05%, e.g. 0.005% to 0.5% boron, the balancebeing essentially nickel, the nickel preferably being at least 56%. Aswill be understood by those skilled in the art, the use of theexpression balance or balance essentially in referring to the nickelcontent of the alloys does not exclude the presence of other elementscommonly present as incidental constituents, e.g. deox-idizing,malleabilizing and/ or cleansing elements, and impurities normallyassociated therewith in small amounts which do not adversely affect thebasic characteristic of the alloys. However, in respect of theconstituents iron, silicon and manganese, the amounts of these elementsshould not exceed 2%, 0.5% and 0.5% respectively; otherwise, the stressrupture and creep properties would be adversely affected. Broadlyspeaking, when the best properties are not required zirconium may beabsent from the alloys as explained hereinafter, and such zirconium-freealloys are in accordance with the invention.

In carrying the invention into practice, if the carbon content of thealloy should fall much below about 0.3% stress-rupture life isconsiderably impaired and the ability to resist excessive creep isadversely affected. On the other hand, if the carbon content exceeds 1%poorer properties are obtained and in particular the ductility andimpact resistance are reduced to unacceptable values. It is quiteadvantageous that the carbon content be from about 0.4% to 0.6%.

With regard to chromium, percentage above 35% adversely affect creepstrength and while the chromium content may be as low as 25%, inachieving the best combination of properties, it is most beneficial thatthe chromium level be not less than about 28%. Where alloys are requiredwhich consistently manifest the best combination of creep strength andcorrosion resistance, a chromium range of 28% to 32% is highlysatisfactory.

Considerable care must also be exercised in respect of tungsten. Whilein many nickel-base and other alloys broad ranges of tungsten can beutilized, that is not the case with the subject alloys. It has beenfound, for example, that even amounts of but 10% (versus the upper limitof about 8%) greatly detract from stress rupture strength and creepresistance. However, tungsten is necessary for hardening the alloys bysolid-solution hardening and by carbide formation and at least about 3%tungsten must be present for this purpose. It is most preferred that thetungsten content not exceed about 6%, and a range of 4% to 6% givesexcellent results. With regard to tantalum, high temperature propertiesare, in the absence thereof, seriously impaired and in this connectionfrom 4% to 5% or 6% tantalum is quite beneficial.

Zirconium confers a most pronounced effect in respect of stress-rupturelife. Amounts as low as about 0.28% have been found to more than doublethe stress rupture life of the alloys at the extremely high temperatureof 1150 C. (approximately 2102 F.). Furthermore, and simultaneouslytherewith (in comparison with a comparable but zirconium-free alloy),this same small amount of zirconium has been found to impart remarkablecreep resistant qualities as will be illustrated herein. However, itappears that as the zirconium content is increased a maximum is reachedin its effectiveness in improving creep strength. The zirconium contentat which the maximum improvement is achieved probably depends on thetemperature at which the alloy is tested or used. Also the choice ofzirconium content may be governed by the need for an optimum combinationof stress-rupture strength and creep resistance. In achieving highlysatisfactory results a zirconium range of about 0.15% to 0.3% or 0.35%is extremely beneficial.

Boron detracts from stress rupture life, as shown by stress rupturetests at 1150 C., and when the best possible stress rupture life isrequired boron should be absent, The presence of boron does, however,enhance the creep resistance of the alloys. For this reason it ispossible to achieve a useful combination of stress rupture strength andcreep resistance by suitably balanced additions of both boron andzirconium. Satisfactory results may be obtained, for example, byincorporating in the alloys from about 0.1% to about 0.5% zirconium andfrom about 0.005% to about 0.05% boron, e.g. from 0.15% to 0.25%zirconium and from 0.01% to 0.03% boron.

A comparison of Alloys A and 1 clearly reflects the subversive influenceattributable to tungsten when appreciably present to the excess. Bothstress rupture life and resistance to creep were greatly adverselyaflfected, the latter by a factor of ten. This damaging effect is evenmore pronounced when the alloy is also low incarbon as can be seen byreference to Alloy B (0.15% carbon vs. 0.5% carbon for Alloy 1.) Thedegradation caused by low carbon is further confirmed by a comparison ofAlloys 2 and C, and 1 and D. Alloys 1 and 2 also indicate that highlysatisfactory results flow from tantalum contents over the range of 3% to6%.

To illustrate the beneficial effects attributable to the presence ofzirconium per se, various data are given in Table II, the alloys beingprepared and tested in the same manner as those set forth in Table I.(Alloys 3 through 8 are within the invention.)

Also included are data concerning the effect of boron.

TABLE II Stress-rupture properties at Creep strain at Composition 11t.s.i./l,150 C. 1.27 t.s.i. 1,080 O.

C Cr W Ta .1" B Life Elongation Time Strain Alloy (percent) (percent)(percent) (percent) (percent) (percent) (hours) (percent) (hours)(percent) 0. 47 29. 5 4. 9 4. 5 2 N.A. N.A 178 13. 2 312 2. 44

0. 49 29. 8 5. 2 4. 6 0.20 N.A 259 14. l 312 0. 54

1 Balance nickel and impurities. 2 N.A. indicates that the element wasnot added.

Alloys in accordance with the invention and containing neither zirconiumnor boron have a fairly satisfac tory stress rupture life but do nothave the excellent creep resistant characteristic of the alloyscontaining zirconium or boron However, the creep properties of thesealloys are adequate for many purposes.

Where resistance to creep is of paramount importance and stress rupturelife can be sacrificed boron, e.g. up to 0.01% or 0.03%, can be presentin the absence of zirconium.

For the purpose of giving those skilled in the art a betterunderstanding of the invention, the following illustrative data aregiven. A series of alloys were vacuum melted in an electric inductionfurnace. Nickel, chromium, tungsten and carbon were first charged intothe furnace and the pressure reduced to 1 micron (of mercury). The pumpwas isolated and the charge melted. After reducing the pressure again,to 5 microns, and holding for minutes, tantalum was added. After holdingfor minutes at 1 micron and 1520 C., zirconium (as nickel-zirconium) orboron (as nickel-boron) or both were added when required in the alloy.The alloys were then cast at 1550 C. into hot refractory molds.Specimens were machined from the alloys and then tested in the as-castcondition and the results are reported in Table I. In this regard andapart from the given amounts (nominal) of carbon, tungsten and tantalumeach of the alloys contained nominally chromium, 0.2% zirconium and0.02% boron, the balance being nickel and impurities. Alloys 1 and 2 arewithin the invention. Alloys A through D being outside the scopethereof. Also set forth in Table I are the conditions of test.

TABLE I The data given in Table 11 indicate the excellent propertieswhich may be obtained in alloys in accordance with the invention. Inthis respect particular attention is drawn to Alloys 4 through 8, whichcontain zirconium. A comparison of Alloys 3 and 5, for example, clearlydemonstrates the potent influence attributable to the presence ofzirconium, rupture life being increased by over 150% with resistance tocreep also being rnarkedly improved. While resistance to creep wasfurther enhanced by the presence of boron, a reduction in stressrupturelife at 1150 C. was experienced.

As discussed herein, where shorter stress rupture lives can betolerated, the alloys may contain boron in the absence of zirconium. Afurther alloy, Alloy 9, is an example of such an alloy. Alloy 9contained 0.49% carbon, 29.8% chromium, 4.9% tungsten, 4.6% tantalum and0.0 15 boron, the balance being essentially nickel. Alloy 9 was preparedand tested in the same manner as the alloys set forth in Table I. After310 hours at 1080 C. under a stress of 1.27 t.s.i. Alloy 9 showed acreep strain of 0.69%.

As indicated above herein, the alloys contemplated herein can beprepared using vacuum techniques. In this connection conventionalmelting and casting techniques can be used in producing the alloys. Toensure retention of a desired amount of any zirconium or boron theseelements should be added to the melt immediately prior to casting.Satisfactorily nickel, chromium, tungsten and carbon are first chargedto the furnace and after melting and holding at less than micronspressure and preferably less than 5 microns pressure for up to 15minutes, e.g. 10 minutes, tantalum is added. The melt Stress ruptureproperties Creep strain at 1.27

2.7 t.S.i. /1,000 C. 1 t.S.i. /1,150 C. t.S.i. /1,08O C.

W Ta Life Elongation Life Elongation Time Strain Alloy (percent)(percent) (percent) (hours) (percent) (hours) (percent) (hours)(percent) 0. 5 10 3 249 312 6. 4 0. 5 5 3 472 310 0. 58 O. 15 1O 3 126197 11. 7 0. 5 5 6 518 310 O. 61 0. 15 5 6 312 6. 7 0. 15 5 3 71 1 Longtons per square inch, 7 H 7 i W 2 Average of two values.

is then held at less than microns pressure and preferably less than 1micron pressure for 10 to 30 or 60 minutes, e.g. minutes, both holdingtreatments being carried out between 1400 and 1600* C. but preferablybetween 1500 and 1550 C., e.g. 1520 C. The duration of the secondholding treatment depends on the purity of the ingredients of the melt,longer time being required when less pure ingredients are employed.Zirconium or boron may then be added, e.g. as nickel-zirconium ornickel-boron. The alloy is then cast at 1500 C. to 1600 C., e.g. at 1530to 1570 C.

Air melting practice may be used if desired but great care should betaken that there is sufiicient zirconium or boron retained when theseelements are required and for this purpose the melt should be deoxidisedimmediately prior to the addition of zirconium or boron.

While the alloys in accordance herewith are useful in applicationsinvolving molten glass (including flowing molten glass), e.g.centrifugal spinners for the manufacture of glass fibre, they can beemployed in many other areas of application where resistance tocorrosion at elevated temperatures in combination with good creep andstress rupture resistance is required, e.g. in industrial chemicalplant.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and appended claims.

I claim:

1. A nickel-base alloy consisting essentially of about 0.3% to about 1%carbon, from to chromium, about 3% to about 8% tungsten, about 2% toabout 8% tantalum, up to about 0.5% zirconium, up to about 0.05% boronand the balance essentially nickel.

2. An alloy in accordance with claim 1 which contains at least 28%chromium.

3 An alloy in accordance with claim 1 in which the tungsten content doesnot exceed 6%.

4. An alloy in accordance with claim 1 containing about 0.4% to about0.6% carbon, about 28% to about 32% chromium, about 4% to about 6%tungsten and about 4% to 6% tantalum.

'5. As a new article of manufacture, a component fabricated from thealloy set forth in claim 1 for use in contact with molten glass.

6. As a new article of manufacture, a component fabricated from thealloy set forth in claim 4 for use in contact with molten glass.

7. A nickel-base alloy consisting essentially of about 0.3% to about 1%carbon, from 25% to 35% chromium, about 3% to about 8% tungsten, about2% to about 8% tantalum, zirconium in a small but effective amountsuflicient to enhance the stress-rupture life of the alloy the amount ofzirconium being up to about 0.5 up to about 0.05% boron and the balanceessentially nickel.

8. An alloy in accordance with claim 7 which contains at least 28%chromium.

9. An alloy in accordance with claim 7 which contains at least 0 .1%zirconium.

10. An alloy in accordance with claim 7 in which the tungsten contentdoes not exceed 6%.

11. An alloy in accordance with claim 7 containing about 0.15% to 0.35%zirconium.

12. An alloy in accordance with claim 7 containing about 0.4% to about0.6% carbon, about 28% to about 32% chromium, about 4% to about 6%tungsten, about 4% to about 6% tantalum and about 0.15 to 0.35zirconium.

13. An alloy in accordance with claim 7 containing from 0.1% to 0.5%zirconium and from 0.005% to 0.05 boron.

14. An alloy in accordance with claim 12 containing from 0.15% to 0.25%zirconium and from 0.01% to 0.03% boron.

15. An alloy in accordance with claim 7 characterized by good stressrupture life and the ability to resist creep at temperatures on theorder of about 1080 C.

16. As a new article of manufacture, a component fabricated from thealloy set forth in claim 7 for use in contact with molten glass.

17. As a new article of manufacture, a component fabricated from thealloy set forth in claim 12 for use in contact with molten glass.

References Cited UNITED STATES PATENTS 3,316,074 4/1967 Laurent et al.75-171 3,318,694 5/1967 Heitmann 75171 RICHARD O. DEAN, Primary ExaminerU.S. Cl. X.R. --1, 15

